@Samuel_H 

Hi, AP mode will not impact the Mesh Performance of Deco.

But no matter whether Deco is on AP mode or router mode, its Wi-Fi Network would still be a different wireless network from the main ISP router's. The Mesh roaming is only within Deco Mesh units. But when they are using the same network name and password, it might decrease the roaming time from the original router to Deco.

Have you ever considered replacing the original router with Deco X50, but still keeping the original network SSID and password on Deco?

Or if the ISP router could not be removed, you could turn off its Wi-Fi and set Deco into AP mode as the only wireless network available.

Thank you very much.

Best regards.